The present invention deals with the fabrication of plastic lumber having sufficient stiffness and strength to allow its use in structural and load-bearing applications. Preferably, the plastic lumber is produced by the combination of a thermoplastic polymer together with a thermosetting polymer containing reinforcing fibers, such as fiberglass, the latter preferably being derived from recycled materials.
It has been well recognized that a use for post-consumer recycled plastics has been in the production of xe2x80x9cplastic lumber.xe2x80x9d Plastic refuse, particularly high density polyethylene (HDPE), such as commonly used to manufacture milk containers, may be recycled and re-molded as increasingly popular plastic-wood fly products. Such a scheme is disclosed in U.S. Pat. No. 5,212,223 wherein an extrudable composition is produced from waste polyolefins which can be made to closely resemble construction lumber. Such waste polyolefins can be derived from a wide variety of consumer products such as picnic tables, park benches, patio furniture and trash receptacles. However, because of the nature of its composition, plastic lumber made from HDPE, PVC, PP, or virgin resins has been characterized as having insufficient stiffness to allow its use in structural load-bearing applications. This deficiency is even more pronounced when plastic lumber is manufactured from waste plastics rather than virgin HDPE. For example, it is noted that non-reinforced plastic lumber products typically have a flexural modulus of only one-tenth to one-fifth that of wood such as Douglas fir.
The above-noted U.S. Pat. No. 5,212,223 discusses the inclusion of short glass fibers within reprocessed polyolefin and further teaches doing so to increase the stiffness of the non-reinforced plastic lumber by a factor of 3:4. However, none of the prior art known to applicant is capable of fabricating plastic lumber having the structural stiffness and strength of products made according to the present invention and having the further advantage in being capable of being fabricated from consumable waste.
The present invention is directed to a plastic lumber product and method for preparing it which is characterized as having sufficient stiffness and strength to allow its use in structural and load-bearing applications. The plastic lumber comprises, in combination, thermoplastic polymer, thermosetting polymer containing reinforcing fibers and, preferable, a coupling agent and a foaming or blowing agent. Ideally, the cured thermosetting polymer containing reinforcing fibers is derived from consumer waste which is characterized as being configured from thermosetting polymers which contain reinforcing fibers, such as fiberglass fibers, together with further additives incorporated therein for the particular use at hand.